Lets draw the Pascal's triangle for n=5:
In Pascal's triangle, each number is the sum of the two numbers directly above it.
By using the last row, we can expand the given expression as
then, the answer is
[tex](x+y)^5=x^5+5x^4y+10x^3y^2+10x^2y^3+5xy^4+y^5[/tex]
